Mr. Offensive, Mr. Defensive

We have an interesting statistical abnormality this season. Looking at the SBC stats, Kamani Johnson is 2nd in offensive boards per game, and Ruot Monyyong is tied for first in defensive rebounds per game. Usually if you have a strong rebounder he will be toward the top in both. (Monyyong is tied for 7th in offensive rebounds.)  I have heard of "designated rebounders," but never "designated offensive rebounders."